The expandable rack bushing guides, cushions and dampens the rack of a rack and pinion vehicle steering system.
The rack of a rack and pinion vehicle steering system is slidably mounted in a rack and pinion housing secured to a vehicle frame. A rack bushing is provided in the rack and pinion housing to guide one end of the rack as it moves parallel to the rack axis. The other end of the rack is supported and guided by rack and pinion engaging teeth. A tie rod assembly is connected to a first end of the rack and to wheel steering arm. A second tie rod assembly is connected to a second end of the rack and to another wheel steering arm.
Wheel steering arms are connected to steered wheels and move with the steered wheels to which they are attached. Since the steered wheels of most vehicles are connected to a vehicle frame by a suspension system there is a substantial range of movement between a wheel steering arm and the steering rack of a rack and pinion steering assembly. To accommodate the movement between a steering arm and a steering rack, a tie rod with ball connectors transmits force between the steering rack and a steering arm. The direction in which force is transmitted to the tie rod by the steering rack is usually at an angle relative to the steering rod axis. Bending loads are therefore applied to the steering rack when the steering rack is moved to change the direction of movement of a vehicle.
Forces are transmitted from road surfaces to tires and wheels, steering arms, tire rods and a steering rack. These forces, that are transmitted to the steering rack, are seldom if ever parallel to the rack axis. The bending loads on a steering rack, that are induced by road surfaces, are variable in both magnitude and direction. The result of the steering rack bending loads is vibrations, noise, gear teeth damage and bushing failures.
Bushings employed with some steering racks tend to slide with the steering rack relative to a rack and pinion housing. The movement of the bushings relative to the housing generates noise, increases wear and eventually results in bushings being forced out of the rack and pinion housing.
The bushings that have been used to support steering racks in rack and pinion housings in the past tend to wipe lubricant from the rack. After lubricant is removed from bushings and bushing contact surfaces on a steering rack, friction forces increase and it takes more effort and strength to turn the steered wheels of a vehicle. A critical side effect of poor lubrication is wear on the rack bushing. Severe wear creates excessive radial clearance, which is a main cause of noise.
The expandable rack bushing has a generally tubular portion with a bushing axis, an outer end and an inner end. A plurality of front slots, in the generally tubular portion, each extend from the outer end toward the inner end and to a front slot end wall. A plurality of rear slots, in the generally tubular portion, each extend from the inner end toward the outer end and to a rear slot end wall. At least some of the rear slot end walls are axially positioned between some of the front slot end walls and the outer end. The slots permit the diameter of the expandable rack bushing to increase. A plurality of spring members on the generally tubular portion absorb forces expanding the generally tubular portion and bias the generally tubular portion toward a non-expanded condition.
A plurality of retainer blocks on the generally tubular portion of the expandable rack bushing extend radially outward from the generally tubular portion. These retainer blocks are received in a groove in a rack housing bore to axially position and retain the rack bushing.